This invention relates to a method and an apparatus for analyzing, by image analysis, textures of coke, pitch, synthetic graphite, sintered ore and other materials containing optically anisotropic textures, and more particularly to a method and an apparatus for quantitative measurement to automatically measure component ratios of the textures.
Coke, for example, contains various textures such as an isotropic texture, an anisotropic texture which shows particle patterns when seen through a microscope, an anisotropic texture which shows fibrous patterns, an anisotropic texture which shows relatively large leaflet patterns, and a texture derived from a coal inert tecture. With coke containing such optically anisotropic textures, these textures are known to be correlated to the blend of coking coals and coking conditions and also to coke performance such as strength, reactivity and so forth. Therefore, coke performance may be presumed from texture analysis data, and moreover such data may be used as control parameters for the blend of coking coals and coking conditions.
In conventional practice, measurement of texture component ratios (or ratios of the textures present) utilizing a microscope generally is carried out manually by the point-counting method. In practising this method an operator operates a polarizing microscope, selects a portion considered to include textures representing the entire field of view, and identifies the textures. This operation is repeated for many fields, preferably 500 or more fields to determine a rate of occurrence of each texture, which forms a basis for determining the texture component ratios in a sample. This conventional method of identifying the textures based on visual observations requires skill and experience and has the problem of exhausting the operators. Moreover, this method is prone to the operators' individual differences which entails poor reproduction of the results. An automatic measurement has been desired to solve these problems.
As far as coal textures are concerned, automatic measuring apparatus associated with a microscope have been developed. One such example is the reflectance measuring system. This system turns intensity of reflected light into a numerical value by means of a photomultiplier and an A/D converter in order to obtain a reflectance, from which the textures are automatically analyzed. However, this system is inapplicable to materials containing anisotropic textures, such as coke because the measured reflectance is primary data and texture identification based thereon lacks in analytic precision. A further method so far proposed for identifying coal textures obtains a microscopic field of image by using a TV camera and determines texture component ratios by a luminance histogram of the image. This method is unsatisfactory from the point of view of precision.
For analyzing the textures of semicoke a method has been proposed in which a polarizing plate adjacent a light source is turned to measure reflectance at certain turning angles and obtain maximum and minimum values thereof. From these values anisotropic indexes are calculated and the textures are classified by threshold levels. However, this method too is unsatisfactory from the point of view of precision.